1. Field of the Invention
The present invention relates to conversion of compressed moving picture data, and more particularly, to a motion vector (MV) estimation method and an encoding mode determining method to convert an input compressed moving picture into another format suitable for a desired frame rate by determining a motion vector and a motion-compensated block type again when the frame rate of the input moving picture needs to be reduced.
2. Description of the Related Art
Several digital contents can be transmitted via various networks such as Internet, wireless networks, and cellular networks. Since these networks have different bandwidths, it is necessary to adapt the bitrates of video streams to bandwidths of the networks in order to be able to provide various multimedia application services through the networks. Rate control methods are often used for application services or encoders. However, in application services such as video on demand (VOD) services, source bitstreams are already compressed at a target bitrate. As a result, there may be no need to perform rate control, depending on the circumstances of the network.
Therefore, scalable video coding methods can be used instead of the rate control methods. The scalable video coding methods adapt the bitrates of video streams to the bandwidth of a network using useful features such as temporal and spatial scalability. However, when using the scalable video coding methods, rate-distortion performance of the scalable video coding methods is degraded because over-head bits are embedded in each scalable level.
To adapt the bitrate of data to be transmitted to the bandwidth of a network, original bitstreams are converted into lower bitrates and thus an effect similar to rate control can be obtained. Transcoders convert compressed data from one format to another. Most transcoders use spatial down-sampling and reduced frame rate transcoding to meet channel bandwidth. In particular, when a small mobile device is considered, it cannot decode the original bitstreams compressed with high frame rates because of low processing power and power consumption. Therefore, a method of changing a frame rate is required.
Also, to provide services such as VOD services, teleconferencing, and distance learning via various networks, a transcoding method and a transcoder that can properly change the frame rate of an image are required.